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UNITED STAT S PATENT OFFICE.

OTTO LIEBKNECHT, OF FRANKFORT-ON-THE'MAIN; GERMANY. ASSIGNOR TO THEROESSLER & HASSLACHER CHEMICAL COMPANY. OF NEW YORK. N. 1., A COR.

PORAIION OF. NEW YORK.

No Drawing.

To all whom it may; concern:

Be it known that I, OTTo LlEBKNl-ICHT, a subject of the German Emperorand resident of Frankforton-thel\[ain, Germany. have invented certainnew and useful lm provements in the Manufacture of Perborates, of whichthe followin is a specification.

It is known that alkali carbonates can be converted by electrolysis intoalkali percarbonat'es, and it is also known that alkali percarbonatescan be again converted into alkali perborates (by double reaction) withborates.

In the matter of a prior application of the same inventor, it has beenshown that the above known process can be successfully can ried out in asingle operation by subjecting a solution which, in addition tocarbonate, contains also borate, to electrolysis in the presence ofsolid perborate.

It is clear that in carrying out such processes on a. manufacturingscale, the tendency should be to replace the expensive platinumelectrodes by a cheaper electrode material. Experiments which theinventor has carried out to that effect, have shown however thatcathodes say of zinc, tin or aluminium which would at fi st sight appearto an expert very suitable, cannot be used because they are attacked byelectric atomizing or chemically by the electrolyte.

in experiments which the inventor made with cathodes of such substanceseasily liable to destruction the surprising discov ery was made that inthe presence of cer tain substances, such as for instance chromic. acidor chromatcs, the cathodes are not attackcd. so that electrolytic manufature of pcrboratcs can be carried out without any disturbance. it forinstance, tin is used as cathode material, a product will be alwaysobtained which is colored gray by finely divided tin and is not verystable owing to the presence of tin. Tf chromic acid is added to theelectrolyte. a white product will he obtained which is Free from tin andtherefore stable. while at; the same time the yield per unit of currentwill be improved as the disturbin; efi ect exercised by liuely dividedtin on the stability of the product is done away with. (hromic acid andchronlaies act in the same way when cathodes of zinc, aluminium. etc,are used.

Specification of Letters Patent.

Patented Nov. 1, [921.

Application filed January 27, 1917. Serial No. 145,917.

on the basis of this discovery it is possible to carry outelectrolysis-of perborates even with substances which under normalconditions are attacked during the electrolysis. Even when usingcathodes which, like those of lead, iron, etc., possess already acomparatively good resistance to the action of the electrolytic liquidduring electrolysis, it has been found advisable to make use of anaddition of chromic acid or of chromates, for the stability of thesesubstances is improved by the resence of such protective substances torte cathodes. In any case the presence of the protecting substances inquestion increases the life of the cathode, insures a smooth course ofthe electrolysis with a better yield and gives a purely white endproduct free from metal.

l hose parts of the cathodes which are not exposed to the current, arepreferably .protected from the action of the electrolytic liqnidin asfar as they are exposed to i[ for instance by covering them with a resistant varnish or by securing to them pieces of substances which arenot corroded. such as for instance Vulcanized rubber.

The present process can be generally ap plied in the electrolytic:manufacture of pcrborate. More particularly, it is not llll')- ited tothe processes described in the prior patent-applications of the sameinventor, which are carried out in the presence of solid perborate,solid hora'x. solid soda.

I claim:

1. ln electrolytic processes with a normally soluble base metal cathode.the step which consists in adding to the electrolyte a [H'OiPPtlIUIsubstance to stabilize the base metal cathode and preventsolution anddeposition thereof in the end product.

S2. in electrolytic processes with a normally soluble base metalcathode, the step which consists in adding to the electrolyte achromium-oxygen compound to stabilize the base metal cathode and preventsolution and deposition thereof in the end product.

fl. In thc electrolytic production of alkali pcrlmrate with a normallysolu le metal rathodc, the stcp which consi ts in adding to theclcctrolyc a prolcctinc substance to sta ilize the base nictul iuil inlt' and pre ent solution and dep sition 4.1.? ml in the product.

4. lo the electr lytic productio: c

bus-

dium perborate with a normally soluble base metal cathode the step whichconsists in adding to the electrolyte a chromium-oxygen compound tostabilize the base metal cathode 5 and prevent solution and depositionthereof the end pl'OdtlCt.

Iii testimony whereof I have signed my name to this specification in thepresence of two SUbSCIiblIlg witnesses.

OTTO LIEBKNECHT.

Witnesses:

HARRY E. CARLSON, J EAN GRUND.

